The present invention relates generally to a polyurethane foam and an associated process for production, and in particular, a polyurethane integral foam and an associated process for production. Polyurethane foams are conventionally produced by mixing a polyisocyanate component of at least one diisocyanate or polyisocyanate with a polyol component of at least one polyether polyol or polyester polyol, in the presence of at least one catalyst and at least one propellant and optionally in the presence of various auxiliaries and additives well known in polyurethane chemistry. These additives also optionally include foam stabilizers.
The properties of the polyurethane foams may be adjusted within wide ranges by use in conjunction with low molecular diols as chain extenders or with triols and amines as crosslinkers.
A special variant of mold foaming is reaction foam casting, which is also referred to as the Reaction Injection Molding (RIM) process. Flexible to semi-hard moldings are obtained from integral foam, which characteristically has a compact edge zone integrally joined to a light cellular core within a molding made from the same PUR material. Such moldings are used, for example, in the automobile industry as car interior covering, dashboards, steering wheels, and also for spoilers, etc. An equally large and important area of application lies in the shoe industry, where such moldings are used for shoe soles or shoe components. PUR foams are used on a large scale today in numerous other areas.
Mainly carbon dioxide or halogen alkanes are used as propellants. Selection of the propellant depends, inter alia, on the reaction mixture to be foamed and the required strength as well as further properties of the final foamed foam. Besides water, fluorochlorohydrocarbons (FCHC), hydrogen fluorochlorohydrocarbons (HFCHC), hydrogen fluorohydrocarbons (HFHC) or special carbamates in particular, have been used as propellants for the production of harder polyurethane foams. Due to the known ecological problems associated with the said halogen-containing propellants, their use is continuously decreasing in the field of integral foams. However, the use of water as exclusive propellant is not a solution to the problems of propellants, particularly because pressure suppression in the foam proceeds considerably more slowly than when using known halogen-containing propellants. As a result, in series production, although there is conventional short remolding times, moldings result which tend to crack easily and the elasticity of the resulting moldings (in particular for shoe soles) does not satisfy the requirements of practice.
Likewise, the obvious concept of using hydrocarbons, such as isomeric pentanes or cyclopentanes, to solve the problems of propellants is undesirable due to the problem of easy flammability of the substances.
Tertiary amines and tin organic compounds generally serve as catalysts for producing polyurethane foams. Tertiary amines are conventionally used for the above-mentioned integral foam systems. Co-catalysis by metal catalysts is possible. The foams produced with the aid of amine catalysts have various disadvantages. The amine catalysts remain in the foam, but are not firmly bound there. Thus, in the course of time, and particularly after high-temperature aging, a long-lasting constant odor results. The gradual gaseous emission of amines may also be associated with health stresses to the user. Accordingly, it is an urgent need of the car industry to have available polyurethane foams which are free of amine emissions, particularly for car interior covering. Furthermore, the foams produced using amine catalysts have the disadvantage that they lead to discoloration of the PVC, particularly when processing as a laminate with PVC. Known amine catalysts have all the afore-mentioned technical disadvantages. They may lead to an unpleasant odor or to PVC discoloration either because they partly evaporate during the reaction or because the curing of the foam is inadequate.
European patent 0 121 850 indeed already describes the use of certain carbamates which carry hydroxyl groups as propellants for polyurethane foams, preferably in combination with other propellants, as can be seen from the exemplary embodiments. However, European patent 0 121 850 does not convey any indication of the surprising finding that carbamates may also be used as catalysts for the production of polyurethane foams. Due to their particular makeup, known carbamates generally cannot also replace the tertiary amine catalysts.
European granted patent 0 652 250 describes the use of carbamates containing hydroxyl groups as exclusive propellant for integral foams. Here too, it is not a question of the replacement of catalysts. Rather, catalysts are thus used which lead to the above-mentioned undesirable accompanying phenomena, such as odor pollution and PVC discoloration.
The present invention is directed to overcoming one or more of the problems set forth above.